Remote-control device



April 14, 1936. R KQCH 2,Q3?,383

REMOTE CONTROL DEVICE Filed Oct. 18, 1930 INVENTOR.

Winfield RKoch,

ATTORNEY.

Patented Apr. 14, 1936 UNITED STATES PATENT OFFICE REMOTE-CONTROL DEVICE Delaware Application October 18,

14 Claims.

My invention relates to remote-control devices and it has particular relation to devices for controlling the tuning of a radio receiving system from a distant point.

There has been, in the radio art, a consistent trend toward the provision of means for remotely controlling the tuning of a radio receiver. For this purpose it has been suggested that the tuning condensers of the receiver be driven synchronously with a remotely disposed indicating device and it'has, further, been proposed to provide the receiving system with a plurality of fixed tuning elements, any one of which can be inserted in circuit through the action of a relay device controlled from a distance.

The first mentioned proposal has met with some success, but its principal disadvantage lies in the high cost of providing the synchronous controldevices; the second system is disadvantageous in that it permits tuning to a limited number only of pre-selected frequencies without permitting the continuous tuning of the system to receive signals from stations transmitting at intermediate frequencies.

It is, accordingly, an object of my inventionto provide means whereby a radio receiving system may be tuned, from a distant point, without resorting to the use of mechanical connections between the system and the tuning-control device.

Another object of my invention is to provide, in a radio receiving system of the remote control type, instrumentalities whereby the tuning of the system shall. be accomplished solely through electrical means.

A still further, and more specific, object of my invention is to provide a radio receiving system of the superheterodyne type having marked stability.

According to a preferred embodiment of my invention, when applied to a radio receiving system of. the superheterodyne type, the local source of oscillations comprises a plurality of tubes so disposed as to constitute a multi-vibrator, so-called. The multi-vibrator, which is described on page 16.? of the Text Book on Wireless Telegraphy by Rupert Stanley, utilizes resistors and capacitors only for frequency-control. Furthermore, although a multi-vibrator is productive of oscillations extremely rich in harmonics, it is also notable for the reason that the frequency of the oscillations generated tends to remainextremely constant.

I have found that, by providing means whereby the effective value of one or more of the resistors or condensers, constituting the inter-tube coupling network of a multi-vibrator, may be changed, the frequency of the generated oscilla- 1930, Serial No. 489,556

tions changes accordingly. I have, therefore, provided means, such as a thermionic tube, whereby the efiective value of a resistor may be controlled from a distance and am thus enabled to continuously tune a superheterodyne receiving system merely by changing the value of the said resistor. Preferablyin a specific embodiment of my invention, the space-current path in the thermionic tube is disposed in shunt to the resistor and means, such as a resistor connected serially with a biasing battery in the grid circuit of the said thermionic tube, is utilized, at the distant control point, to alter the conductivity of the tube by changing the grid-biasing potential applied thereto.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The, invention itself, however, both, as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of certain specific embodiments when read in connection with the accompanying drawing, in which:

Fig, 1 is a schematic view of a radio receiver of the superheterodyne type, comprising a preferred embodiment of my invention, and

Fig. 2 is a schematic view of an alternative embodiment of myinvention as applied to an oscillation generator.

Referring specifically to Fig. 1 of the drawing, a radio receiving system, constructed according to my invention, preferably comprises a balanced first detector stage I, constituted by a plurality of thermionic devices 3 and 5 of the shield-grid type, having a common untuned input circuit, constituted by an inductor 1, and a common output inductor 8, a plurality of intermediate-frequency amplifying tubes 9, II and I3, a second detector tube l5, and a power amplifying stage ll including a plurality of thermionic devices l9 and 2| disposed in push-pull relation.

The input inductor l of the detector stage is coupled to an antenna 23 through a filter 25, one output terminal of which is connected to an intermediate point on the inductor, and the other terminal ofwhich is connected, through a condenser 21, to a conductor 29 common to the cathodes of the first detector tubes 3 and 5.

The local oscillator comprises a plurality of thermionic tubes 3| and 33 inter-connected for regeneration through a network constituted by a plurality of coupling condensers 35 and 37 and a plurality of grid-leaks 39 and 4|, and supplied with plate potential over a plurality of resistors 42.

The oscillation generator is of the type commonly known as a multi-vibrator, and produces oscillations that are rich in harmonic frequencies. It is, accordingly, expedient to so choose the magnitudes of the condensers and resistors constituting the coupling network between the oscillator tubes that the fundamental frequency generated is comparatively low, use being made of one of the higher harmonics, the eighth for example, for heterodyning purposes. In order that the undesired harmonics shall not be impressed upon the input circuit of the first detector stage I, a band-pass filter 43, of any well known type, is interposed between the multivibrator and the said detector stage, the output terminals of the filter being connected to the grids of the first detector tubes 3 and 5, respectively. The constants of the filter are such that frequencies between 11,500 and 12,500 kilocycles are transmitted thereby.

All of the thermionic devices in the system, with the exception of those included in the power amplifier stage, are preferably of the equipotential cathode type and are supplied with plate, shield-grid and control-grid biasing potentials from a resistor 45 that is connected across any convenient source (not shown) of uni-directional current.

In order that a measure of volume control may be had, I find it expedient to connect the controlgrids of the first two intermediate-frequency amplifier tubes 9 and II to the movable contact 46 of a potentiometer 41, the terminals of which are connected to points on the resistor 45 that are maintained at minus 3 and minus 50 volts, respectively. The potentiometer is, preferably, included as a constituent part of a remote control device indicated generally by a dotted rectangle As is explained in the text book hereinbefore referred to, the fundamental frequency of the oscillations generated by the multi-vibrator is a function of the magnitudes of the grid-leaks, the coupling condensers and the resistors over which potential is applied to the plates of the thermionic tubes from a common source. I have discovered that a variation in the effective values of certain of these elements may be utilized .to cause the fundamental frequency to vary within limits sufliciently wide to enable signal-frequencies lying in the entire broadcast band to be heterodyned to the beat frequency to which the intermediate stages of the receiver are tuned.

I have also discovered that if the space-current path of a thermionic tube is effectively connected in parallel to one of the resistors in the multivibrator system, any variations in the plate impedance of the said thermionic tube is reflected in a change in the frequency of the oscillations generated.

I have, accordingly, connected the anode of a thermionic device 5| to the grid of the tube 33 in the multi-vibrator by way of a coupling condenser 53, which offers low impedance to currents at radio frequency, and I have provided a grid biasing battery 55, a fixed resistor 56, and a variable resistor 51, whereby the potential of the grid of the said thermionic device may be caused to so vary as to alter the plate impedance of the device to the desired amount. The resistor 51 is preferably disposed within the same receptacle that houses the volume-control potentiometer 41, the resistor andpotentiometer being connected to the radio receiving system proper through a plurality of conductors 59, 6|, 62, 63 and 65, of any desired length.

In a preferred commercial embodiment of my invention, the resistors 42 each have a resistance of 10,000 ohms, the coupling condensers 35 and 31, a capacity of 25 micro-microfarads each, the grid-leak 39, a resistance of 2,500 ohms, and the grid-leak 4|, a resistance of 100,000 ohms. The grid-biasing battery 55 for the thermionic controltube 5| has a potential of 45 volts, the resistor 51 is variable from 0 to 100,000 ohms, while the fixed resistor 56, the drop across which determines the grid-bias potential applied to the grid of the thermionic tube 5|, has a resistance of 10,000 ohms. The plate-impedance of the thermionic tube 5|, in the system under discussion, may be caused to vary from 2,000 ohms to 1,000,000 ohms or more by adjustment of the variable resistor and the fundamental frequency of the multivibrator, namely, 1,500 kilocycles, may be altered plus or minus 60 kilocycles by adjusting the said resistor. I

In the operation of my improved receiving system, for the reception of signals lying in the present broadcast band, namely, 550 to 1500 kilocycles, an incoming signal, after being partially freed from disturbing frequencies by the input bandpass filter 25, is impressed in phase upon the grids of the tubes 3 and 5 constituting the first detector stage. Since these tubes are provided with the common output inductor 8, having an intermediate tap through which plate potential is applied to the tubes, the output currents therefrom are balanced, when the local oscillator is not in operation, and no signal is impressed upon the intermediate frequency amplifier 9, which, in a preferred embodiment of my invention, is tuned to a beat frequency of substantially 11,000 kilocycles and passes a band of frequencies lying 5 kilocycles above and below the said beat frequency.

Inasmuch, however, as the locally generate oscillations are impressed out of phase upon the grids of the detector tubes, by reason of'the connection thereto of the terminals of the filter network 43, the said oscillations and the incoming signal combine to give rise to -a beat frequency which carries the signal modulation. Since the intermediate frequency stages are tuned to a definite beat frequency it is clear that, by altering the frequency of the locally generated oscillations, the tuning of the system, considered as a whole, may be effectively changed. In order, therefore, to shift the tuning of the system from one frequency to another, it is merely necessary to actuate the variable resistor 51 to change the amount of current fio-wing through the fixed resistor 56 which, in turn, changes the biasing potential applied to the grid of the thermionic tube 5|.

Since the plate impedance of the tube 5| is a function of the grid-biasing potential, any change in the said potential alters the impedance of the space-current path of the tube, which is connected in shunt relation to the resistor 4|. As previously pointed out, the frequency of the oscillations generated is a function of the magnitudes of the resistors 33 and 4| and, since the effective value of the resistor 4| is controlled by the tube 5|, any change in the magnitude of the remote-control resistor 51 results in a change in the frequency.

It will thus be apparent that I have, by my invention, provided a remote-control system for .a radio receiver that is devoid of mechanical parts such asrotating armatures and the like.

Cir

Neither the radio frequency of the received signal nor the oscillations of the multi-vibrator are conveyed to the point of remote control where the variable resistor 51 is located. This remote control circuit may, therefore, be termed a signal-free circuit, meaning that it is devoid of the impress thereon of signals whether the modulated incoming signals or those of the multivibrator which are unmodulated. My improved system is also relatively inexpensive to manufacture and is capable of exact pre-calibration.

Since one of the important phases of my invention is concerned with the provision of a multi-vibrator as a source of local oscillations in a superheterodyne receiver, it lies within the scope thereof to control the frequency of the generated oscillations by means other than those heretofore described. For example, as illustrated inFig. 2 of the drawing, the thermionic tube 5i may be dispensed with and a plurality of resistors H, l2, 13, 15, and ll, be so disposed with respect to the grid and cathode of the tube 33 that any one of them may be interposed in circuit at will.

In order that any desired one of the said resistors may be utilized, I find it expedient to employ a selector device constituted by a stepping magnet 19 and a movable armature 8|, such as is commonly used in automatic telephone systems, and to control the stepping magnet by a dialing device 83 situated at a remote point.

Each of the resistors is given a fixed value cor responding to a definite oscillation frequency and the receiving system, therefore, may be effectively tuned to any one of a plurality of pre-selected transmitting stations merely by causing the proper resistor to be included in circuit.

It also lies within the scope of my invention to invert the control tube 5| that is, to connect the grid to the blocking condenser instead of connecting the plate thereto, and to connect the plate to' the biasing battery 55, making use of a potentiometer for the latter connection, if desirable. Furthermore, an additional control tube may be supplied to vary the grid-resistance of the oscillator tube 3|, and it and the tube 5! may be simultaneously or individually utilized for frequency-control.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof will be apparent to those skilled in the art to which it pertains. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In a signal receiving system, a local variable frequency source of oscillations having a frequency-determining resistance-element, means for deriving a beat frequency from the oscillations produced by said local source and an incoming signal, and means for remotely controlling the effective value of said resistance element.

2. In combination, means including a detector for receiving incoming signals, an oscillation generator of the multi-vibrator type comprising a frequency-determining impedance-element, a combining network for heterodyning the frequencies of said incoming signals and of said oscillation generator, a space discharge tube having its space-current path connected in parallel with said frequency-determining element, and means including an adjustable resistor remote from said tube for varying the conductivity of said space-current path.

3. In a signal receiving system, an oscillation generator of the multi-vibrator type having a frequency determining element, means for deriving a beat frequency from the oscillations generated thereby and an incoming radio signal, a thermionic tube having its space-current path connected in parallel to the frequency-determining element of said oscillation generator, and means including a source of grid bias potential and a variable resistor for remotely controlling the plate-impedance of said thermionic tube.

4. In a signal receiving system an oscillation generator of the multi-vibrator type having a frequency-determining impedance element, means for deriving a beat frequency from the oscillations generated thereby and an incoming radio signal, a thermionic tube having its spacecurrent path connected in parallel with said impedance-element, and remotely situated means for varying the grid-biasing potential applied to said thermionic tube, whereby the frequency of the generated oscillations may be controlled and the receiving system made receptive to incoming signals of a desired frequency.

5. In a signal receiving system of the superheterodyne type an oscillation generator of the multi-vibrator type constituted by a plurality of thermionic tubes inter-connected by way of a esistance-condenser network, a plurality of gridleak resistors and means for connecting any one of said resistors between the grid and cathode of 1 caused to heterodyne with incoming signals of a desired frequency.

7. In a signal receiving system, an oscillation generator of the multi-vibrator type, means for deriving a beat frequency from the oscillations generated by said generator and an incoming signal, filter means interposed between said generator and said deriving means for excluding undesired harmonic frequencies, and extensible signal-free means for adjusting said oscillator to beat with the frequency of a desired incoming signal.

8. In a superheterodyne signal receiving system, the combination of a detector stage, a source of signals, a filter connected between said signal source and said detector stage, and means for tuning said system, including an oscillation generator of the multi-vibrator type having a frequency determining impedance element, a band-pass filter connected between said oscillation generator and said detector stage, a thermionic tube having its space-current path connected in parallel with said impedance element, and a remote control circuit including a variable impedance element connected with said thermionic tube to vary its space-current.

9. In a superheterodyne signal receiving system, the combination of a detector stage, including an input inductor and a pair of thermionic tubes connected thereto in push pull relation, a source of signals, a filter connected between said signal source and said detector stage, said filter being of the band-pass type adapted to remove signals at frequencies outside a normal predetermined band, and means for tuning said system, including an oscillation generator of the multi-vibrator type having a frequency determining impedance element, a band-pass filter connected between said oscillation generator and said detector stage, said filter having a characteristic and being so connected with the push pull detector stage that oscillation voltages from said oscillation generator are impressed in outof-phase relation upon the input electrodes of said push pull connected thermionic tubes, a thermionic tube having its space-current path connected in parallel with said impedance element, and a remote control circuit including a variable impedance element connected with said thermionic tube to vary its space-current.

10. In a superheterodyne receiver, the combination of a detector tuned to respond to a band of signals between certain predetermined frequency limits, and a multi-vibrator oscillator connected with the detector to provide with said signals a beat frequency signal, said oscillator having a frequency control circuit, a frequency determining impedance element in said circuit, and means including a space discharge tube and a capacitor connected between the output circuit thereof and said impedance element, said space discharge tube having a remote control device connected thereto for varying the effective impedance value of said element.

11. In a superheterodyne receiver, the combination of a detector tuned to respond to a band of signals between certain predetermined frequency limits, and a multi-vibrator oscillator connected with the detector to provide with said signals a beat frequency signal, said oscillator having a frequency control circuit, a frequency determining impedance element in said circuit, an electron discharge device having its space current path connected in parallel with said frequency determining element, and means including a remotely situated adjustable resistor for varying the conductivity of said space current path.

12. In a superheterodyne receiver, the combination of a detector tuned to respond to a band of signals between certain predetermined frequency limits, and a multi-vibrator oscillator connected with the detector to provide with said signals a beat frequency signal, said oscillator having a frequency control circuit, a frequency determining impedance element in said circuit, an electron discharge device having its space current path connected in parallel with said impedance element, and means for varying the grid biasing potential applied to said device whereby the frequency of the generated oscillations may be controlled.

13. In a signal receiving system of the superheterodyne type, tuning control means therefor comprising an oscillation generator of the multivibrator type, an impedance element for determining the frequency of the oscillations generated by said generator, a signal-free remote control circuit for varying the effective value of said impedance element, a signal receiving circuit, a detector connected with said signal receiving circuit and with said oscillator to derive a beat frequency from said oscillations and an incoming signal, and a band pass filter interposed in each of said connections with the detector.

14. In a signal receiving system of the superheterodyne type, tuning control means therefor comp-rising an oscillation generator of the multivibrator type, said generator having a non-resonant control circuit responsive to changes in impedance for changing the frequency of the oscillations generated thereby, an impedance selecting switch for said circuit, a remote control circuit and means for transmitting impulses through said remote control circuit to actuate said switch.

WINFIELD RUDOLPH KOCH. 

